Re: [PATCH v2 1/6] iommu/vt-d: Setup scalable mode context entry in probe path

[Baolu Lu]

On 12/8/23 4:50 PM, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Tuesday, December 5, 2023 9:22 AM
> >
> > @@ -304,6 +304,11 @@ int intel_pasid_setup_first_level(struct intel_iommu
> > *iommu,
> >   		return -EINVAL;
> >   	}
> >
> > +	if (intel_pasid_setup_sm_context(dev, true)) {
> > +		dev_err(dev, "Context entry is not configured\n");
> > +		return -ENODEV;
> > +	}
> > +
> >   	spin_lock(&iommu->lock);
> >   	pte = intel_pasid_get_entry(dev, pasid);
> >   	if (!pte) {
> > @@ -384,6 +389,11 @@ int intel_pasid_setup_second_level(struct
> > intel_iommu *iommu,
> >   		return -EINVAL;
> >   	}
> >
> > +	if (intel_pasid_setup_sm_context(dev, true)) {
> > +		dev_err(dev, "Context entry is not configured\n");
> > +		return -ENODEV;
> > +	}
> > +
> >   	pgd = domain->pgd;
> >   	agaw = iommu_skip_agaw(domain, iommu, &pgd);
> >   	if (agaw < 0) {
> > @@ -505,6 +515,11 @@ int intel_pasid_setup_pass_through(struct
> > intel_iommu *iommu,
> >   	u16 did = FLPT_DEFAULT_DID;
> >   	struct pasid_entry *pte;
> >
> > +	if (intel_pasid_setup_sm_context(dev, true)) {
> > +		dev_err(dev, "Context entry is not configured\n");
> > +		return -ENODEV;
> > +	}
> > +
> >   	spin_lock(&iommu->lock);
> >   	pte = intel_pasid_get_entry(dev, pasid);
> >   	if (!pte) {
>
> instead of replicating the invocation in all three stubs it's simpler to
> do once in dmar_domain_attach_device() for all of them.

It's not good to repeat the code. Perhaps we can add this check to
intel_pasid_get_entry()? The rule is that you can't get the pasid entry
if the context is copied.

> Then put the deferred check outside of intel_pasid_setup_sm_context()
> instead of using a Boolean flag

Okay, that's more readable.

> > @@ -623,6 +638,11 @@ int intel_pasid_setup_nested(struct intel_iommu
> > *iommu, struct device *dev,
> >   		return -EINVAL;
> >   	}
> >
> > +	if (intel_pasid_setup_sm_context(dev, true)) {
> > +		dev_err_ratelimited(dev, "Context entry is not configured\n");
> > +		return -ENODEV;
> > +	}
> > +
>
> Do we support nested in kdump?

No.

> > +
> > +	/*
> > +	 * Cache invalidation for changes to a scalable-mode context table
> > +	 * entry.
> > +	 *
> > +	 * Section 6.5.3.3 of the VT-d spec:
> > +	 * - Device-selective context-cache invalidation;
> > +	 * - Domain-selective PASID-cache invalidation to affected domains
> > +	 *   (can be skipped if all PASID entries were not-present);
> > +	 * - Domain-selective IOTLB invalidation to affected domains;
> > +	 * - Global Device-TLB invalidation to affected functions.
> > +	 *
> > +	 * For kdump cases, old valid entries may be cached due to the
> > +	 * in-flight DMA and copied pgtable, but there is no unmapping
> > +	 * behaviour for them, thus we need explicit cache flushes for all
> > +	 * affected domain IDs and PASIDs used in the copied PASID table.
> > +	 * Given that we have no idea about which domain IDs and PASIDs
> > were
> > +	 * used in the copied tables, upgrade them to global PASID and IOTLB
> > +	 * cache invalidation.
> > +	 *
> > +	 * For kdump case, at this point, the device is supposed to finish
> > +	 * reset at its driver probe stage, so no in-flight DMA will exist,
> > +	 * and we don't need to worry anymore hereafter.
> > +	 */
> > +	if (context_copied(iommu, bus, devfn)) {
> > +		context_clear_entry(context);
> > +		clear_context_copied(iommu, bus, devfn);
> > +		iommu->flush.flush_context(iommu, 0,
> > +					   (((u16)bus) << 8) | devfn,
> > +					   DMA_CCMD_MASK_NOBIT,
> > +					   DMA_CCMD_DEVICE_INVL);
> > +		qi_flush_pasid_cache(iommu, 0, QI_PC_GLOBAL, 0);
> > +		iommu->flush.flush_iotlb(iommu, 0, 0, 0,
> > DMA_TLB_GLOBAL_FLUSH);
> > +		devtlb_invalidation_with_pasid(iommu, dev,
> > IOMMU_NO_PASID);
> > +	}
>
> I don't see this logic from existing code. If it's a bug fix then
> please send it separately first.

This code originates from domain_context_mapping_one(). It's not a bug
fix.

> > +
> > +	context_entry_set_pasid_table(context, dev);
>
> and here is additional change to the context entry. Why is the
> context cache invalidated in the start?

The previous context entry may be copied from a previous kernel.
Therefore, we need to tear down the entry and flush the caches before
reusing it.

> > +
> > +static int pci_pasid_table_setup(struct pci_dev *pdev, u16 alias, void *data)
> > +{
> > +	struct device *dev = data;
> > +
> > +	if (dev != &pdev->dev)
> > +		return 0;
>
> what is it for? the existing domain_context_mapping_cb() doesn't have
> this check then implying a behavior change.

Emm, I should remove this line and keep it consistent with the exiting
code.

Best regards,
baolu